(1) Field of the Invention
The present invention relates to a method of and a device for writing and reading optical data on an optical data writing medium (hereinafter referred to as optical disk), and more particularly to a method of and a device for writing and reading data by using a phase transition medium.
(2) Description of the Related Art
In an optical disk device, data is written on an optical disk by irradiating the disk with a laser beam. The irradiation of the optical disk with the laser beam results in a local temperature rise in a writing film of the optical disk due to light absorption. The local temperature rise causes changes in the state of the writing film, thus enabling the writing.
In the optical disk device, it is necessary, during the signal writing, to verify whether the writing data has been correctly written on the optical disk. In a prior art optical disk device, which is commercially available at present, the verification of writing data is made by reading the written area after the writing. In other prior art examples, a plurality of light sources are used, or a plurality of beam spots formed by diffraction grating are used, as disclosed in Japanese Patent Application Kokai Publication No. Hei 2-9024 or Japanese Patent Application Kokai Publication No. Hei 3-41632, whereby one or more beam spots are used for the verification. With respect to a magneto-optical disk, there is a proposal as disclosed in Japanese Patent Application Kokai Publication No. Hei 5-144112in which a single beam verification using a single beam spot, is realized by utilizing characters unique or inherent to an opto-magnet.
In the prior art verification methods applied to the optical disk devices described above, there have been problems that, in the case where the verification is made after the writing operation, the time required for the writing is extended. In the case where a plurality of beam spots are used, there have been problems that the cost is high and the adjustment of optical system is difficult. With the phase transition type optical disks in which the writing and reading principles are different from those in the magneto-optical disk, a method for realizing a single beam verification using a single beam spot verification has not heretofore been known.